Study of the pretreatment and hydrolysis of a mixture of coffee husk, cowpea bean husk and cocoa pod for bacterial cellulose production

Agro-industrial solid residues (AISR) need to be valued as rich sources of nutrients and energy. This work aimed to obtain reducing sugars (RS) from a mixture of coffee husk (CF), cowpea bean husk (BE) and cocoa pod (CO) to produce bacterial cellulose (BC), a versatile alternative to plant cellulose. The most adequate conditions for pretreatment followed by enzymatic hydrolysis were selected with the Design of Experiments statistical tool for, respectively, a first solid load of 10% (w/v) of a mixture of CF:BE:CO = 2:8:2 in 0.25% (v/v) H₂SO₄, followed by a second solid load of 20% (w/v) in sodium citrate buffer [pH = 4.8 and] with 10 FPU/mg of cellulases. A hydrolysate was obtained, after 48 h of hydrolysis, containing 54.45 ± 2.61% (w/w) of glucose with a cellulose digestibility of almost 87%. This hydrolysate was added to nutrients and 20 g of pure glucose and was used in the cultivation of Komagataeibacter hansenii ATCC 23769 and resulted in BC = 179.00 ± 33.95 g/L (w. b.). These results encourage the biotechnological use of different AISR in mixtures to produce RS in order to obtain valuable materials, such as BC.